Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already mark this as read-only, idempotent, and non-destructive; the description adds meaningful non-obvious behavior beyond that: the request charges nothing, wrong credentials return specific errors (401/403), and the account balance excludes product daily credits. No contradiction with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is long but every clause carries information, including error cases and credential routing. It is front-loaded with the core action and return contents; a slight readability cost comes from packing all caveats into two long sentences.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Coupled with an existing output schema and annotations that already establish read-only/idempotent behavior, the description covers authentication, pricing, error behavior, and credit semantics. Nothing needed for correct invocation is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Although the schema covers the parameter well, the description adds crucial provenance and precedence: the secret must come from sign_up, a client-config data key is not sufficient, and if both are supplied the secret argument wins. This is information an agent cannot infer from the schema alone.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with 'Reads the account behind the secret', a specific verb plus a clearly bounded resource, then enumerates the principal data returned (terms version, products, balance, usage, movements). It also distinguishes itself from list_products by pointing out where product-specific credit accounts live, so an agent can tell sibling tools apart.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives concrete when-to/not-to guidance: it tells the agent the secret must come from sign_up, that the client configuration's data key will not work and yields 403, and that a missing string yields 401. It also directs product-level credit inquiries to list_products, making the boundary between the two tools explicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.